Uplink power headroom reporting for carrier aggregation

ABSTRACT

A method for reporting power headroom is disclosed. Power headroom may be reported across all carriers (wideband), for a specific carrier, or for a carrier group. The formula used to calculate the power headroom depends on whether the carrier (or a carrier in the carrier group) has a valid uplink grant. If the carrier or carrier group does not have a valid uplink grant, the power headroom may be calculated based on a reference grant. The power headroom is calculated by a wireless transmit/receive unit and is reported to an eNodeB.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/119,471, filed Dec. 3, 2008, and U.S. Provisional Application No.61/119,790, filed Dec. 4, 9008, which axe incorporated by reference asif fully set forth herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

This disclosure relates to uplink (UL) power headroom (PH) reporting forcarrier aggregation in wireless communications, in particular withreference to Long Term Evolution Advanced (LTE-A). Power headroom is thedifference between a wireless transmit/receive unit's (WTRU's) maximumtransmit power and the estimated power for a physical UL shared channel(PUSCH) transmission in the current subframe. A power headroom report(PHR) is an index reported by the WTRU to indicate the estimated PH. TheWTRU sends the PHR to an evolved Node B (eNodeB or eNB), which may usethe PHP to determine how much more UL bandwidth per subframe the WTRU iscapable of using.

To support higher data rates and spectrum efficiency, the 3GPP long termevolution (LTE) system has been introduced into 3GPP Release 8 (P8). Tofurther improve achievable throughput and coverage of LTE-based radioaccess systems, and to meet the International Mobile Telecommunications(IMT)-Advanced requirements of 1 Gbps and 500 Mbps in the downlink (DL)and UL directions respectively, LTE-Advanced (LTE-A) is currently understudy in the 3GPP standardisation body.

The LTE DL transmission scheme is based on an orthogonal frequencydivisional multiple access (OPDMA) air interface. For the LTE ULdirection, single-carrier (SC) transmission based on discrete Fouriertransform (DFT)-spread OFDMA (DFT-S-OFDMA) is used. The use ofsingle-carrier transmission in the UL is motivated by the lower peak toaverage power ratio (PAPR) or cubic metric (related to the non-linearityof a power amplifier) of the signal as compared to a multi-carriertransmission scheme such as OFDM.

For flexible deployment, LTE systems support scalable transmissionbandwidths of either 1, 4, 3, 5, 10, 15, or 20 MHz. The LTE system mayoperate in either frequency division duplex (FDD), time division duplex(TDD), or half-duplex FDD modes.

In an LTE system, each radio frame (10 ms) consists of ten equally sizedsub-frames of 1 ms. Each sub-frame consists of two equally sizedtimeslots of 0.5 ms each. There may be either seven or six OFDM symbolsper timeslot. Seven symbols are used with a normal cyclic prefix length,and six symbols per timeslot in an alternative system configuration maybe used with an extended cyclic prefix length. The sub-carrier spacingfor the LTE system is 15 kHz. An alternative reduced sub-carrier spacingmode using 7.5 kHz is also possible. A resource element (EE) correspondsto precisely one sub-carrier during one OFDM symbol interval. Twelveconsecutive sub-carriers during a 0.5 ms timeslot constitute oneresource block (RB). Therefore, with seven symbols per timeslot, each RBconsists of 12×7=84 REs. A DL carrier may consist of a scalable numberof resource blacks (RBs), ranging from a minimum of six RBs up to amaximum of 110 RBs. This corresponds to an overall scalable transmissionbandwidth of roughly 1 MHz up to 20 MHz, but a set of commontransmission bandwidths is usually specified, e.g., 1.4, 3, 5, 10, 15,or 20 MHz. The basic time-domain unit for dynamic scheduling in LTE isone sub-frame consisting of two consecutive timeslots. This is referredto as an RB pair. Certain sub-carriers on some OFDM symbols areallocated to carry pilot signals in the time-frequency grid. A givennumber of sub-carriers at the edges of the transmission bandwidth arenot transmitted to comply with the spectral mask requirements.

In the DL direction, a WTRU may be allocated by an eNodeB to receive itsdata anywhere across the whole transmission bandwidth, e.g., an OFDMAscheme is used. The DL has an unused direct current (DC) offsetsub-carrier in the center of the spectrum.

In the UL direction, LTE is based on DFT-S-OFDMA, or equivalently,SC-FDMA transmission. The purpose is to achieve a lower PAPR compared tothe OFDMA transmission format. Conceptually, whereas in the LTE DLdirection, a WTRU may receive its signal anywhere across the frequencydomain in the whole LTE transmission bandwidth, a WTRU in the UL maytransmit only on a limited contiguous set of assigned sub-carriers in anFDMA arrangement. This principle is called single carrier (SC)-FDMA. Forexample, if the overall OFDM signal or system bandwidth in the UL iscomposed of sub-carriers numbered 1 to 100, a first WTRU may be assignedto transmit its own signal on sub-carriers 1-12, a second WTRU maytransmit on sub-carriers 13-24, and so on. An eNodeB receives acomposite UL signal across the entire transmission bandwidth from one ormore WTRUs at the same time, but each WTRU may only transmit into asubset of the available transmission bandwidth. In principle, DFT-S OFDMin the LTE DL may therefore be seen as a conventional form of OFDM transmission with the additional constraint that the time-frequency resourceassigned to a WTRU consists of a set of frequency-consecutivesub-carriers. In the LTE UL, there is no DC sub-carrier (unlike the DL).Frequency hopping may be applied in one mode of operation to ULtransmissions by a WTRU.

One improvement proposed for LTE-A is carrier aggregation and supportfor flexible bandwidth. One motivation for these changes is to allow DLand UL transmission bandwidths to exceed the 20 MHz maximum of R8 LTE,e.g., to allow a 40 MHz bandwidth. A second motivation is to allow formore flexible usage of the available paired spectrum. For example,whereas R8 LTE is limited to operate in symmetrical and paired FDD mode,e.g., DL and UL are both 10 MHz or 20 MHz in transmission bandwidtheach, LTE-A may operate in asymmetric configurations, such as DL 10 MHzpaired with UL 5 MHz. In addition, composite aggregate transmissionbandwidths may also be possible with LTE-A, e.g., in the DL, a first 20MHz carrier and a second 10 MHz carrier paired with an UL 20 MHz carrierand so on. The composite aggregate transmission bandwidths may notnecessarily be contiguous in the frequency domain, e.g., the first 10MHz component carrier in the above example may be spaced by 22.5 MHz inthe DL band from the second 5 MHz DL component carrier. Alternatively,operation in contiguous aggregate transmission bandwidths may also bepossible, e.g., a first DL component carrier of 20 MHz is aggregatedwith a contiguous 10 MHz DL component carrier and paired with a ULcarrier of 20 MHz.

Examples of different configurations for LTE-A carrier aggregation andsupport for flexible bandwidth are illustrated in FIG. 1. FIG. 1 adepicts three component carriers, two of which are contiguous and athird which is not contiguous. FIGS. 1 b and 1 c both depict threecontiguous component carriers. There are two options for extending theLTE R8 transmission structure/format to incorporate the aggregatedcomponent carriers. One option is to apply the OFT precoder to theaggregate bandwidth, e.g., across all the component carriers in case thesignal is contiguous, as shown in FIG. 1 b and the right side of FIG. 1a. A second option is to apply the DFT precoder per component carrieronly, as shown in FIG. 1 c. It is noted that different carriers may havedifferent modulation and coding sets (MCSs; i.e., a carrier-specificMCS), as shown in FIG. 1 c.

In the ES LTE system UL direction, WTRUs transmit their data (and insome cases their control information) on the PUSCH. The PUSCHtransmission is scheduled and controlled by the eNodeB using the ULscheduling grant, which is carried on physical DL control channel(PDCCH) format 0. As part of the UL scheduling grant, the WTRU receivescontrol information including the modulation and coding set (MCS),transmit power control (TPC) command, UL resource allocation (i.e., theindices of allocated resource blocks), etc. The WTRU transmits its PUSCHon the allocated UL resources with the corresponding MCS at the transmitpower controlled by the TPC command.

For scheduling UL WTRU transmissions, the scheduler at the eNodeB needsto select an appropriate transport format (i.e., MCS) for a certainresource allocation. For this, the scheduler needs to be able toestimate the UL link quality for the scheduled WTRU.

This requires that the eNodeB has knowledge of the WTRU's transmitpower. In LTE, the estimated WTRU transmit power is calculated accordingto a formula where the eNodeB has knowledge of all components in theformula except for the WTRU's estimate of the DL pathloss. In LTE, aWTRU measures and reports back its DL pathloss estimate to the eNodeB inthe form of a PH measurement reporting quantity. This is similar to theconcept of PH reporting in wideband code division multiple access(WCDMA) Release 6, where the PH is also reported for the eNodeB toperform, appropriate UL scheduling.

In LTE, the PIT reporting procedure is used to provide the servingeNodeB with information about the difference between the WTRU's transmitpower and the maximum WTRU transmit power (for positive PH values). Theinformation may also include the difference between the maximum WTRUtransmit power and the calculated WTRU transmit power, according to theUL power control formula, when it exceeds the maximum WTRU transmitpower (for negative PH values).

As explained above, in LTE, a single component carrier is used;therefore the definition of WTRU PH is based on one carrier. The WTRUtransmit power P_(PUSCH) for the PUSCH transmission in subframe i isdefined by:

P _(PUSCH)(i)=min{P _(CMAX),10 log_(t0)(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(j)+α(j)×PL+Δ _(TF)(i)+f(i)}  Equation (1)

where P_(CMAX) is the configured maximum, allowed WTRU transmit power.P_(CMAX) depends on the WTRU power class, allowed tolerances andadjustments, and a maximum allowed transmit power signaled to the WTRUby the eNodeB.

M_(PUSCH)(i) is the bandwidth of the PUSCH resource assignment expressedin the number of resource blocks valid for subframe i.

P_(O) _(—) _(PUSCH)(j) is the sum of a cell-specific nominal componentP_(O) _(—) _(NOMINAL) _(—) _(PUSCH)(j) and a WTRU specific-componentP_(O) _(—) _(UE) _(—) _(PUSCH)(j). P_(O) _(—) _(NOMINAL) _(—)_(PUSCH)(j) is signaled from higher layers for j=0 and 1 in the range of[−126,24] dBm with 1 dB resolution and P_(O) _(—) _(DE) _(—) _(PUSCH)(j)is configured by radio resource control (RRC) for j=0 and 1 in the rangeof [−8, 7] dB with 1dB resolution. For PUSCH (re)transmissionscorresponding to a configured scheduling grant, j=0 and for PUSCH(re)transmissions corresponding to a received PDCCH with DCI format 0associated with a new packet transmission, j=1. For PUSCH(re)transmissions corresponding to the random access response grant,j=2. P_(O) _(—) _(UE) _(—) _(PUSCH)(2)=0 and P_(O) _(—) _(NOMINAL) _(—)_(PUSCH)(2)=P_(O) _(—) _(PRE)+Δ_(PREAMBLE) _(—) _(Msg3), where P_(O)_(—) _(PRE) and Δ_(PREAMBLE) _(—) _(Msg3) are signaled from higherlayers.

For j=0 or 1, αε{0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a three bitcell-specific parameter provided by higher layers. For j=2, α(j)=1.

PL is the DL pathloss estimate calculated by the WTRU.

Δ_(TF)(i)=10log_(t0)((2^(MPR×K) ^(s) −1)×β_(offset) ^(PUSCH)) forK_(s)=1.25 and Δ_(TF)(i)=0 for K_(s)=0, where K_(s) is a WTRU-specificparameter given by RRC.

${MPR} = \frac{O_{CQI}}{N_{RE}}$

for control data sent via the PUSCH without UL shared channel (UL-SCH)data, where O_(CQI) is the number of CQI bits, including CRC bits, andN_(RE) is the number of resource elements.

${MPR} = {\sum\limits_{r = 0}^{C - 1}\frac{K_{r}}{N_{SE}}}$

for other cases, where C is the number of code blocks and K_(s) is thesize for code block r. β_(offset) ^(PUSCH)=β_(offset) ^(CQI) for controldata sent via the PUSCH without UL-SCH and β_(offset) ^(PUSCH)=1 forother cases.

f(i)=δ_(PUSCH)(i−K_(PUSCH)) it accumulation of TPC commands is notenabled based on the WTRU-specific parameter Accumulation-enabledprovided by higher layers, δ_(PUSCH) is a WTRU-specified correctionvalue, also referred to as a TPC command and is signaled to the WTRU inthe PDCCH. K_(PUSCH) is a subframe offset such that the value of f(i) inthe current subframe i is the δ_(PUSCH) value received K_(PUSCH) framesbefore the current frame i. For FDD, K_(PUSCH)=4 and for TDD, the valueof K_(PUSCH) varies.

The WTRU PH for subframe i is defined by:

PH(i)=P _(CMAX)−{10log_(t0)(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(j)+α×PL+Δ _(TF)(i)+f(i)}  Equation (2)

The WTRU transmit power for the PUSCH in subframe i required by the ULscheduling grant (including radio bearer (RB) allocation, MCS, and powercontrol command) without taking into account any maximum transmit powerlimitations, is denoted as P_(PUSCH) _(—) _(UG)(i), and is defined as

P _(PUSCH) _(—) _(UG)(i)=10log_(t0)(M _(PUSCH)(i))+P _(O) _(—)_(PUSCH)(j)+α(j)×PL+Δ _(TP)(i)+f(i)  Equation (3)

Then, the actual WTRU transmit power on the PUSCH in Equation 1 may berewritten as:

P _(PUSCH)(i)=min{P _(CMAX) , P _(PUSCH) _(—) _(UG)(i)}  Equation 4)

The PH formula for LTE in Equation 2 may be rewritten as:

PH(i)=P _(CMAX) −P _(PUSCH) _(—) _(UG)(i)  Equation (5)

The existing definition of PH in LTE has been designed for the specificcase of the SC-FDMA (or DFT-S OFDMA) am interface provided by R8 LTE. Assuch, it specifically applies to only one component carrier and onlyresults in one single value measured and reported back by a WTRU for itsentire UL direction and for a single multiple access scheme (onetransmit antenna: SC-FDMA). But this approach is not applicable to anLTE-A system using carrier aggregation, new multiple access schemes,MIMO schemes, or when operating in flexible bandwidth arrangements,where the eNodeB needs to know the PH information for multiple componentcarriers and/or multiple power amplifiers (PAs) to schedule and assignUL transmissions for the WTRU with the appropriate transmit powerlevels.

For example, suppose that three carriers are aggregated and used in anLTE-A system. The WTRU may have different maximum transmit powers ondifferent carriers or have different pathloss values and/or open looppower control parameters leading to different transmit power levels ondifferent carriers. At one sub-frame, the eNodeB may schedule the WTRUto transmit on two carriers (e.g., carriers 1 and 2). Given that the twocarriers have different transmit powers, a single PH value would not beable to indicate the difference between the WTRU's maximum transmitpower and the calculated transmit power (according to the power controlformula) on each of the two carriers. Furthermore, when the eNodeB wantsto schedule a future UL transmission on carrier 3, it will not know thePH information on carrier 3 (because the PH may not be reported,according to the concept in LTE). If carrier 3 is not contiguous tocarriers 1 and 2, the DL pathloss on carrier 3 may not be derivedreliably from the PH on carriers 1 and 2. The pathloss difference innon-contiguous carrier aggregation may be large, such as greater than 7or 9 dB. This makes it difficult for the eNodeB to schedule ULtransmissions with optimised power levels because the WTRU measured andreported PH value is not a representative metric equally valid for allthe UL carriers assigned to that WTRU.

In addition to the existing reported PH values not being sufficient toaccommodate multiple carriers, the signaling related to PH repeating isalso insufficient. In an LTE system, transmission by the WTRU of asingle value PHR for the entire cell bandwidth is triggered in one ofthe following ways: periodically (controlled by the PERIODIC_PHR_TIMER),if the pathloss has changed more than DL_PathlossChange dB since thelast PHR and a predefined time has elapsed since the last report(controlled by the PROHIBIT_PHR_TIMER), or upon configuration andreconfiguration of a periodic PHR. Even if multiple events occur by thetime a PHR may be transmitted, only one PHR is included in the MACprotocol data unit (PDU).

Methods and procedures are needed to estimate and report representativePH information when multiple carriers are assigned to a WTRU in an LTE-Asystem incorporating carrier aggregation. Furthermore, the transmissionand signaling of the PH information also needs to be addressed tosupport efficient PH reporting in LTE-A.

SUMMARY

A method for reporting power headroom is disclosed. Power headroom maybe reported across all carriers (wideband), for a specific carrier, orfor a carrier group. The formula used to calculate the power headroomdepends on whether the carrier (or a carrier in the carrier group) has avalid uplink grant. If the carrier or carrier group does not have avalid uplink grant, the power headroom may be calculated based on areference grant. The power headroom is calculated by a wirelesstransmit/receive unit and is reported to an eNodeB.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIGS. 1 a-1 c show different example configurations for LTE-A carrieraggregation;

FIG. 2 is a flowchart of a method for wideband PH reporting;

FIG. 3 is a flowchart of a method for carrier-specific or carriergroup-specific PH reporting;

FIG. 4 shows an LTE wireless communication system/access network; and

FIG. 5 is an exemplary block diagram of the LTE wireless communicationsystem of FIG. 4.

DETAILED DESCRIPTION

When referred to hereafter, the term “wireless transmit/receive unit(WTRU)” includes, but m not limited to, a user equipment (UE), a mobilestation, a feed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (FDA), a computer, or any othertype of user device capable of operating in. a wireless environment.When referred to hereafter, the term “base station” includes, but is notlimited to, an eNode B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

The maximum transmit power of a WTRU may be limited by any combinationof the following: WTRU power class definition, allowed value or valuesprovided by higher layer configuration, or limitation by the WTRU'sPA(s). The eNodeB may configure the maximum WTRU transmit power percarrier, per carrier group, or for all carriers using higher layersignaling (e.g., ERG signaling).

With regard to carrier grouping, one grouping method is such thatcontiguous carriers are grouped together. A second method is such thatwhen multiple carriers share the same PA, the carriers may be a group.If the WTRU has different PAs controlling different UL carriers, thenthe WTRU may need to report the PA association with the carriers atinitial network access (RRC connection, setup), handover (RRC connectionreconfiguration), or other RRC reestablishment events.

Alternatively, the PA association with the carriers (i.e., CC-to-PAmapping) may be provided by the eNodeB via higher layer signaling if themapping is determined in the eNodeB. For example, consider the case of aWTRU transmitting on J component carriers (CCs) (where J≧1) using L PAs(where L≧1). The mapping of J CCs to L PAs may be signaled by the WTRUto the eNodeB, if the mapping is determined In the WTRU. Alternatively,the mapping maybe signaled by the eNodeB to the WTRU if the mapping isdetermined in the eNodeB. Alternatively, the mapping may beindependently derived by both the WTRU and the eNodeB based onpre-defined rules that are a function of configuration, such as WTRUcategory and/or carrier allocation. The number of the PAs at the WTRUmay be derivable by the eNodeB from the WTRU category informationsignaled, for example, by the WTRU as part of the WTRU capabilityinformation. Alternatively, the WTRU may explicitly signal the number ofPAs and their characteristics, e.g., maximum transmit power, to theeNodeB.

Defining and calculating the PH needs to reflect the difference betweenthe WTRU maximum transmit power and the calculated WTRU transmit poweraccording to the UL power control formula which can be defined forspecific carriers, across carriers associated with distinct PAs, oracross all carriers. Three basic scenarios are defined for the maximumtransmit power limitation. For each of these scenarios, methods forcalculating and reporting the PH are provided. PH calculations andreporting are performed by the WTRU.

Scenario 1

The sum of the WTRU's transmit power on all aggregated carriers issubject to a pre-defined and/or configured maximum transmit power,P_(CMAX). As in LTE, P_(CMAX) may depend on some combination of the WTRUpower class, allowed tolerances and adjustments, and a maximum allowedtransmit power (possibly per carrier group) signaled to the WTRU by theeNodeB. This scenario could correspond to the case where there is onlyone radio frequency (RF) PA controlling WTRU transmit signalamplification/power on all aggregated carriers or a maximum transmitpower is configured for all carriers by higher layer signaling. In thisscenario, the sum of the WTRU's transmit power on all aggregatedcarriers is limited to P_(CMAX).

Method 1.A

In this method, the wideband PH for the WTRU in subframe i is definedas:

$\begin{matrix}{{{PH}_{WB}(i)} = {P_{CMAX} - {10\; \log_{10}\left\{ {\sum\limits_{k \in \Omega}10^{\frac{P_{PUSCH\_ UG}{({k,i})}}{10}}} \right\}}}} & {{Equation}\mspace{14mu} (6)}\end{matrix}$

where k is a carrier number in a range of k=1, . . . , K, Ω is the setof active carriers (each having a UL grant for subframe i), andP_(PUSCH) _(—) _(UG)(k,i) is the transmit power for the PUSCH to betransmitted on carrier k in subframe i prior to taking into accountpower limitations. The PH is computed by the WTRU for a particulartransmission, based on the current UL grant(s) to the WTRU, wheredifferent UL grants may be allocated to different carriers.

When the eNodeB changes the UL grant, either by increasing or decreasingthe amount of bandwidth available to the WTRU or the modulation andcoding set (MCS) level, the eModeB knows the available power of the WTRUbased on the reported PH. This wideband PH reporting has a benefit ofminimizing signaling overhead by reporting a single value.

Method 1.B

In this method, a PH per carrier is defined. For each UL carrier k thathas a valid UL grant (and therefore has a PUSCH transmission) insubframe i, its PH is defined as:

PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—)_(UG)(k,i)  Equation (7)

where P_(CMAX) _(—) _(carrier)(k) is the configured maximum WTRUtransmit power of the k-th carrier, which may be defined as:

$\begin{matrix}{{{P_{CMAX\_ carrier}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{{k = 1},K,K}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}}\mspace{20mu} {or}} & {{Equation}\mspace{14mu} \left( {7\; a} \right)} \\{{P_{CMAX\_ carrier}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k = \Omega}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}} & {{Equation}\mspace{14mu} \left( {7\; b} \right)}\end{matrix}$

where BW_(k) is the bandwidth for carrier k. The definition of P_(CMAX)_(—) _(carrier)(k) in Equation 7a is used for ail sub-bands or carriers(k=1, . . . , K) across all PAs at the WTRU. The definition of P_(CMAX)_(—) _(carrier)(k) in Equation 7b is used for the subset of carriers(i.e., the carriers in the set Ω), for example, that share the same PA.When each carrier has the same bandwidth, P_(CMAX) _(—) _(carrier)(k) isidentical for all the carriers of interest. Alternatively, P_(CMAX) _(—)_(carrier)(k) may be configured differently or independently for eachcarrier k, but the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers kor k in Ω is subject to the total maximum transmit power P_(CMAX), thatis

${\sum\limits_{{k = 1},K,K}{P_{{CMAX}\_ {carrier}}(k)}} \leq P_{CMAX}$

for Equation (7a) and

${\sum\limits_{k \in \Omega}{P_{{CMAX}\_ {carrier}}(k)}} \leq P_{CMAX}$

for Equation (7b). alternatively, P_(CMAX) _(—) _(carrier)(k) may be setto a constant value for all k for simplicity.

As described above, the PH may be calculated by the WTRU based on thecurrent UL grant given to the WTRU for each UL component carrier, wherethe UL grant is provided to the WTRU by the eNodeB. Equation 7 is forthis case. Alternatively, if no current grant is given, a recent orlatest UL grant may be used instead in the same equation. Alternatively,the PH may be calculated by using a reference UL scheduling grant ratherthan being based on the actual grant. For example: PH_(RG)(k,i)=P_(CMAX)_(—carrier) (k)−P_(PUSCH) _(—) _(BG)(k,i), where P_(PUSCH) _(—)_(RG)(k,i) is the transmit power that may be determined based on areference grant allocation in carrier k in which an UL transmission ismade. The reference grant is an assumption that the WTRU and the eNodeBpreviously agree upon (e.g., pre-defined, signaled) as a reference touse when reporting the PH.

For each UL carrier k that has no UL grant, the WTRU may optionallyreport its PH, which is determined based on reference grant parameters(PUSCH assignment, transport format, etc.) as follows:

PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—)_(REF)(k,i)  Equation (8)

where P_(PUSCH) _(—) _(REF)(k,i) is defined as

P _(PUSCH) _(—) _(REF)(k,i)=f ₁ _(—) _(REF)(P _(PUSCH) _(—)_(REF)(n,i))+α×(PL(k)−f ₂ _(—) _(REF)(PL(n)))  Equation (9)

where n≠k and carrier n belongs to the set of carriers with a validuplink grant, α is a cell-specific parameter. PL(k) is the pathlossestimate calculated by the WTRU on carrier k. If the variance in thepathloss between different carriers is not significantly different(e.g., less than 1 dB), a single PL value for the carriers may be usedfor simplicity. Carrier n belongs to the set of carriers with a valid ULgrant, f₁ _(—) _(REF)(*) is a function of a reference carrier-specificWTRU transmit power, and f₂ _(—) _(REF)(*) is a function of a referencecarrier-specific pathloss. The reference functions may be, but are notlimited to, any one of the following: a fixed value reference,parameters of one of the UL carriers that have a valid UL grant, or anaverage value of parameters of all UL carriers that have a valid ULgrant.

Method 1.C

In this method, a PH per group of carriers is defined. In particular,contiguous carriers or carriers sharing the same PA may be groupedtogether. Suppose that a carrier group m has a set of carriers denotedas Ω_(m). For each UL carrier group m that has a UL grant for at leastone of the carriers in the group, its PH is defined as:

$\begin{matrix}{{{PH}\left( {m,i} \right)} = {{10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} (10)}\end{matrix}$

where P_(CMAX) _(—) _(carrier)(k) is defined as in Equations 7a or 7b.For a particular carrier without a valid UL grant, its transmit powermay be zero (i.e., P_(PUSCH) _(—) _(UG)(k,i)=0 for carrier k that doesnot have a UL grant in subframe i).

For each UL carrier group m that has no UL grant for any carrier in thegroup, the PH for the carrier group may be determined and reported basedon reference grant parameters as:

$\begin{matrix}{{{PH}\left( {m,i} \right)} = {{10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {REF}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} (11)}\end{matrix}$

Typically, carrier group-specific PH reporting may be used for the casewhere carriers within a group are contiguous (and possibly have similarUL grants) so that their transmit power levels are close to each other(leading to PH values being similar to each other). With carriergroup-specific PH reporting, the PH reporting overhead is less than thatwith carrier-specific PH reporting.

Method 1.D

Combining the wideband and carrier (or carrier group) specific methodsmay be used. For example: reporting wideband PH and carrier-specific PHvalues, or reporting wideband PH and carrier group-specific PH values.

There may be advantages to a combined reporting, which depend on thenature of the communication within the eNodeB. If each carrier istransmitted separately, possibly with its own UL grant, there may be abenefit of providing a total transmit power measurement (through thewideband PH report) along with a carrier-specific transmit powermeasurement (through the CC specific PH report). By using a combinedreport, the eNodeB may obtain this information without requiringadditional internal processing of the PH report within the eNodeB. TheeNodeB may configure each WTRU with respect to how the WTRU reports thePH (e.g., either reporting wideband PH, per-carrier PH, per-carriergroup PH, or a combination of them).

Scenario 2

The total WTRU transmit power on carrier group m is subject to apre-defined and/or configured maximum transmit, power P_(CMAX)(m), whereP_(CMAX)(m) is the configured maximum allowed WTRU transmit power (indBm) for carrier group m. P_(CMAX)(m) may depend on some combination ofthe WTRU power class, allowed tolerances and adjustments, and a maximumallowed transmit power (possibly per carrier group) signaled to the WTRUby the eNodeB. A carrier group may consist of one or more carriers. Onereason for several carriers being configured as a carrier group is thecase of multiple carriers associated with one RF PA. Alternatively, thegrouping of earners may be configured, for example, by the eNodeB viahigher layer signaling, without regard to the carrier-PA association.

Let Ω_(m) denote the set of carriers in the carrier group m. For aparticular carrier without a valid UL grant, its transmit power may bezero (i.e., P_(PUSCH) _(—) _(UG)(k,i)=0 for carrier k that does not havea UL grant in subframe i).

Method 2.A

In this method, the wideband PH for the WTRU in subframe i is definedas:

$\begin{matrix}{{{PH}_{WB}(i)} = {{10\; {\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} \left( {12a} \right)} \\{\mspace{79mu} {or}} & \; \\{{{{PH}_{WB}(i)} = {{10\; {\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{m}{\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}}} \right)}}}}\mspace{20mu} {{Alternatively},}} & {{Equation}\mspace{14mu} \left( {12b} \right)} \\{{{PH}_{WB}(i)} = {{10\; {\log_{10}\left( {\frac{1}{M}{\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}} & {{Equation}{\mspace{11mu} \;}\left( {13a} \right)} \\{\mspace{79mu} {or}} & \; \\{{{PH}_{WB}(i)} = {{10\; {\log_{10}\left( {\frac{1}{M}{\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{m}{\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}}} \right)}}}} & {{Equation}\mspace{14mu} \left( {13b} \right)}\end{matrix}$

where M is the number of carrier groups.

The WTRU may optionally report a wideband PH for the carriers without aUL grant, which is denoted as PH_(WB) _(—) _(NG)(i).

$\begin{matrix}{{{PH}_{{WB}\_ {NG}}(i)} = {{10\; {\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega}10^{\frac{P_{{PUSCH}\_ {REF}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} (14)}\end{matrix}$

where P_(PUSCH) _(—) _(REF)(k,i) is as defined previously. Recallingthat k is a carrier number, where k=1, . . . , K, and Ω is the set ofactive carriers (each having a UL grant for subframe i), the computed ULpower in Equation 14 is a summation over the subset of carriers in theset of k=1, . . . , K, that are not in the set of active carriers Ω.

Method 2.B

In this method, a PH per carrier group is defined. For each UL carriergroup m that has a valid UL grant for one or more carriers in the group(and therefore has a PUSCH transmission) in subframe i, its PH isdefined as:

$\begin{matrix}{{{PH}\left( {m,i} \right)} = {{P_{CMAX}(m)} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} (15)}\end{matrix}$

where P_(CMAX)(m) is as defined previously.

For each UL carrier group m that has no UL grant for any carrier in thegroup, the WTRU may optionally report its PH, which is defined based onreference grant parameters (PUSCH assignment, transport format, etc.)as:

$\begin{matrix}{{{PH}\left( {m,i} \right)} = {{P_{CMAX}(m)} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {REF}}{({k,i})}}{10}}} \right)}}}} & {{Equation}\mspace{14mu} (16)}\end{matrix}$

where P_(PUSCH) _(—) _(REF)(k,i) is defined as in Equation 9.

As mentioned previously, carrier group-specific PH reporting may be usedtypically for the case where carriers within a group are contiguous (andpossibly have similar UL grants) so that their transmit power levels areclose to each other (leading to PH values being similar to each other).

Method 2.C

In this method, a PH per carrier is defined. For UL carrier k in Ω_(m)that has a valid UL grant (and therefore has a PUSCH transmission) insubframe i, its PH is defined as:

PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—)_(UG)(k,i)  Equation (17)

where P_(CMAX) _(—) _(carrier)(k) is the configured maximum WTRUtransmit power of the k-th carrier in Ω_(m), which may be defined as:

$\begin{matrix}{{P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega_{m}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}} & {{Equation}\mspace{14mu} \left( {17a} \right)} \\{\mspace{79mu} {or}} & \; \\{{P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in {\Omega_{m}\bigcap\; {carrierkhasgrant}}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}} & {{Equation}\mspace{14mu} \left( {17b} \right)}\end{matrix}$

where the summation in Equation 17b is applied only for carriers in thecarrier group, each carrier having a UL grant.

When each carrier has the same bandwidth, P_(CMAX) _(—) _(carrier)(k) isthe same for all the carriers in Ω_(m). Alternatively, P_(CMAX) _(—)_(carrier)(k) may be configured differently or independently for eachcarrier k, but the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers kin Ω_(m) is subject to the carrier group maximum transmit powerP_(CMAX)(m), that is

${\sum\limits_{k \in \Omega_{m}}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}(m)}$

for Equation 17a or

${\sum\limits_{k \in {\Omega_{m}\bigcap\; {carrierkhasgrant}}}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}(m)}$

for Equation 17b. Alternatively, P_(CMAX) _(—) _(carrier)(k) may be setto a constant value for all k in Ω_(m) for simplicity.

For each UL carrier k that has no UL grant, the WTRU may optionallyreport its PH, which is defined based on reference grant parameters(PUSCH assignment, transport format, etc.) as:

PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—)_(REF)(k,i)  Equation (18)

where

${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega_{m}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}$

and P_(PUSCH) _(—) _(REF)(k,i) is defined as in Equation 9.

Method 2.D

A combination of the wideband and the carrier (or carrier group)specific methods may be used. For example: reporting wideband PH andcarrier-specific PH values, or reporting wideband PH and carriergroup-specific PH values. The eNodeB may configure each WTRU withrespect to bow the WTRU reports the PH (e.g., either reporting widebandPH, per-carrier PH, per-carrier group PH, or a combination of them).

Method 2.E

In this method, the PH calculation is based on a reference carrier. Aspathloss is dependent on carrier frequency (i.e., the higher the carrierfrequency, the larger the pathloss), reporting the PH is based on areference component carrier, for example, the carrier having the lowestcarrier frequency or the carrier having the highest carrier frequency.Power headroom values for the other carriers are calculated and reportedrelative to the reference carrier. Alternatively, the WTRU reports a PHfor the reference carrier and the eNodeB estimates the PH for the othercarriers according to the reported reference PH. This method is alsoapplicable to Scenarios 1 and 3.

Scenario 3

The total WTRU transmit power on carrier group m is subject to apre-defined and/or configured maximum, transmit power P_(CMAX)(m).P_(CMAX)(m) may depend on some combination of the WTRU power class,allowed tolerances and adjustments, and a maximum allowed transmit power(possibly per carrier group) signaled to the WTRU by the eNodeB. Theremay be one or more carriers in the carrier group. Furthermore, the sumof the WTRU transmit power on all aggregated carriers is subject to apre-defined and/or configured maximum allowed transmit power P_(CMAX)_(—) _(total), where

$P_{{CMAX}\_ {total}} \leq {10\; {\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}\mspace{14mu} {or}}$$P_{{CMAX}\_ {total}} \leq {10\; {{\log_{10}\left( {\sum\limits_{{k = 1},K,K}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}.}}$

P_(CMAX) _(—) _(total) may depend on some combination of the WTRU powerclass, allowed tolerances and adjustments, and a maximum allowedaggregate transmit power signaled to the WTRU by the eNodeB. Thisscenario could correspond to the ease where there is a RF PA controllingWTRU transmit signal amplification/power for a group of one or multiplecarriers, a maximum transmit power is configured for each carrier group,and a maximum transmit power is configured for all carriers (or carriergroups).

For convenience of discussion, similar to Equation 3, P_(PUSCH) _(—)_(UG)(k,i) is used to denote the WTRU transmit power in subframe i oncarrier k required by a given UL scheduling grant (RB allocation, MCS,power control command, etc.) before taking into account any maximumtransmit power limitations. The exact formula of P_(PUSCH) _(—)_(UG)(k,i) in LTE-A depends on the power control procedures and formulaadopted by the LTE-A standards. In the remaining discussion, theproposed methods are independent of UL power control procedures and theformula used to determine P_(PUSCH) _(—) _(UG)(k,i).

It is assumed herein that there are K aggregated carriers in the UL,where K≧1. Among the K carriers, M carriers (where M≦K) have valid ULgrants in subframe i. Let Ω denote the set of all the carriers withvalid UL grants.

Method 3.A

In this method, the wideband PH for the WTRU for subframe i is definedin Equation 6. This wideband PH reporting has a benefit of minimisingsignaling overhead by reporting a single value. The WTRU may optionallyreport a wideband PH on a carrier without an UL grant, which is denotedas P_(PUSCH) _(—) _(UG)(k,i) as defined in Equation 14.

Method 3.B

In this method, a PH per carrier is defined. For each UL carrier k thathas a valid UL grant (and therefore has a PUSCH transmission) insubframe i, its PH is defined in Equation 17, furthermore subject to

$P_{{CMAX}\_ {total}} \leq {10\; {{\log_{10}\left( {\sum\limits_{{k = 1},K,K}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}.}}$

For each UL carrier k that has no UL grant, the WTRU may optionallyreport its PH, which is defined based on reference parameters (PUSCHassignment, transport format, etc.) in Equation 18, furthermore subjectto

$P_{{CMAX}\_ {total}} \leq {10\; {{\log_{10}\left( {\sum\limits_{{k = 1},K,K}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}.}}$

Method 3.D

In this method, a PH per carrier group is defined. For each UL carriergroup m that has a valid UL grant for at least one carrier in the group(and therefore has a PUSCH transmission) in subframe i, its PH isdefined in Equation 15, furthermore subject to

$P_{{CMAX}\_ {total}} \leq {10\; {{\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}.}}$

For each UL carrier group m that has no UL grant for any carrier in thegroup, the WTRU may optionally report its PH, which is defined based onreference grant parameters (PUSCH assignment, transport format, etc.) inEquation 16, furthermore subject to

$P_{{CMAX}\_ {total}} \leq {10\; {{\log_{10}\left( {\sum\limits_{m}10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}.}}$

Method 3.D

A combination of wideband and carrier (or carrier group) specificmethods may be used. For example, reporting wideband PH andcarrier-specific PH values or reporting wideband PH and carriergroup-specific PH values. The eNodeB may configure each WTRU withrespect to how the WTRU reports the PH (e.g., either reporting widebandPH, per-carrier PH, per-carrier group PH, or a combination of them).

Power Headroom with Consideration of Cubic Metric

In the UL of LTE-A, the single carrier property may be lost due toseveral factors including carrier aggregation, enhanced multiple accesstechniques (such as OFDMA or cluster-based DPT-OFDMA), and MIMO. Asignal without the single carrier property may typically have a largercubic metric (CM) than a signal with the single carrier property.Transmitting a signal with such a higher CM, could, depending on WTRU RFPA characteristics, require some degree of derating or backoff fromnominal maximum power. To avoid occurrences of the WTRU backing off fromnominal maximum power, the PH reporting may include the effect of thehigher CM. For example, for the case given in Equation 15 in Method 2.B,the CM may be factored into the PH calculation using:

$\begin{matrix}{{{PH}\left( {m,i} \right)} = {{P_{CMAX}^{\prime}(m)} - {10 \times \log \; 10\left\{ {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right\}}}} & {{Equation}\mspace{14mu} (19)}\end{matrix}$

where P′_(CMAX) _(—) _(L)−T(P′_(CMAX) _(—) _(L))≦P′_(CMAX)≦P_(CMAX) _(—)_(H)+T(P_(CMAX) _(—) _(H)), P′_(CMAX) _(—) _(L)=min(P_(EMAX) _(—)_(L,)P_(UMAX)−ΔCM(i)), P′_(CMAX) _(—) _(H)=min(P_(EMAX) _(—)_(H),P_(powerCmax)). P_(EMAX) _(—) _(L) and P_(EMAX) _(—) _(H),respectively, are the maximum allowed power configured by higher layers,P_(UMAX) is the WTRU maximum output power, depending on the WTRU powerclass and/or PA implementation. P_(PowerClass) is the WTRU maximumoutput power, depending on the WTRU power class, without taking intoaccount the tolerance or any backoff. P′_(CMAX) is a modification ofP_(CMAX) as defined previously, in effect lowering the lower bound ofP_(CMAX) given that it is bounded by P_(UMAX) rather than by P_(EMAX)_(—) _(L). ΔCM(i) is a factor related to the higher CM (typically in dB)due to loss of the single carrier property in subframe i. ΔCM(i) isdetermined by the WTRU by any known method, taking into account thegiven PA implementation. For a WTRU with more than one PA, the methodmay be unique for each PA.

Statistic-Based Power Headroom Reporting

With multiple PH values to be reported, the PHR signaling overhead inLTE-A increases compared to that of LTE. To save control signaling, anefficient PHR signaling may be used.

To reduce overhead, a reduced member of PH values may be signaled. Thegoal of reporting PH is to let the network know how mush the power maybe set for an UL transmission. It may be difficult to select aparticular per-carrier PHR to signal to the network, because the currentPHR definition depends on the UL scheduling grant, differences inpathloss, and limitations on different PAs. For example, if the grant incarrier 1 is larger than the grant in carrier 2, the PHR in carrier 1may be smaller than in carrier 2 even if the pathloss in carrier 1 issmaller.

To reduce overhead, a statistic of the multiple carrier group (orcarrier) specific PHRs may be used. For example, the statistic may beany one of: the smallest PH from the set, the PH corresponding to thelargest pathloss carrier, or the PH corresponding to the smallestpathloss carrier (P_(CMAX) _(—) _(carrier)-pathloss). By selecting thePHR that corresponds to the smallest pathloss carrier, it effectivelyremoves the grant dependent aspect from the PHR selection.

A statistical measure of the individual PHRs may be used. As an example,the mean of the PHs or the worst-case PH may be reported. In addition tothis statistical measure, differential PH values for individual carriersmay also be reported.

Differential Reporting

To save control signaling overhead, differential PH reporting may beused. For example, for Method 2.B, one or several carriers' PH valuesmay be reported with full resolution and set as reference points. The PHvalues for the rest of the carriers may be computed and reporteddifferentially (i.e., as a delta) with respect to reference points.Another example is that in Method 2.D, the wideband PH values may beused as reference points, then carrier group-specific PH values may becomputed and reported differentially with respect to the wideband PHvalue.

The signaling format for a full-resolution PHR (used as reference point)may be kept the same as that for LTE R8, i.e., six bits with the range[40; −23] dB with a resolution, of 1 dB, so that backward compatibilitymay be maintained. Differential PHR may be reported with fewer bits.

Mapping of Power Headroom Reporting in the Uplink

In LTE, the PH is carried in a medium access control (MAC) controlelement (CE) on the PUSCH on the UL carrier (since it has only onecarrier). For LTE-A, there may be several PH values to be reported.Therefore, the mapping of the PHR to the UL carrier(s) has to bespecified.

When only one type of PHR is triggered m a given sub-frame ortransmission time interval (TTI), any one of the following PHR to ULcarrier mappings may be used.

1. Carrier-specific PHR (for a carrier with an UL grant) is transmittedon its own UL carrier.

2. Carrier-specific PHR (for a carrier without an UL grant) istransmitted on a predefined UL carrier.

3. Carrier group-specific PHR (for a carrier group with an UL grant) istransmitted on a carrier within the carrier group.

4. Carrier group-specific PHR (for a carrier group with an UL grant) istransmitted on a carrier according to a predetermined rule.

5. Wideband PHR is mapped on one carrier according to a predefined rule.

When more than one type of PHR is triggered in a given sub-frame or TTI,the PHR for the carrier (or carriers/carrier group) without an UL grantmay be transmitted on the same carrier as a PHR for a carrier (orcarriers/carrier group) with an UL grant. Wideband PHR with an UL grantmay be transmitted on the same carrier as the carrier-specific orcarrier group-specific PHR with grant or vice versa.

Reporting Modes of Power Headroom

There are several types of PH information. Wideband PH (WB-PHR) includesone WB-PHR for all carriers with a valid UL scheduling grant in thecurrent TTI (Type 1) or one WB-PHR for all carriers without a valid ULscheduling grant in the current TTI (Type 2). Carrier-specific orcarrier group-specific PH (CS-PHR) includes one CS-PHR for each carrieror carrier group with a valid UL scheduling grant in the current TTI(Type 3) or one CS-PHR for each carrier or carrier group without a validUL scheduling grant in the current TTI (Type 4).

The system may support several PH reporting modes, which may beconfigured and reconfigured by the eNodeB via RRC signaling or L1/L2signaling. The PH reporting for LTE-A with carrier aggregation may beany one or a combination of aforementioned types. For example, thefollowing reporting modes are possible depending on the UL multipleaccess scheme, the UL power control scheme, and whether the maximum WTRUtransmit power limit is per carrier or across all carriers:

Report mode 1: Type 1 PH only

Report mode 2: Type 3 PH only

Report mode 3: Types 1 and 3 PH

Report mode 4: Types 1 and 2 PH

Report mode 5: Types 3 and 4 PH

Report mode 6: Types 1, 2, and 3 PH

Report mode 7: Types 1, 3, and 4 PH

Report mode 8: Types 1, 2, 3, and 4 PH

Configuration of Power Headroom Reporting Procedures

Reporting parameters (PERIODIC PHR TIMER, DL_PathlossChange, andPROHIBIT_PHR_TIMER) used for different types of PH may be configured tocontrol the reporting frequency for each type of PH. For PH Type i(where i=1, 2, 3, or 4), the parameters PROHIBIT_PHR_TIMER(i), PERIODICPHR TIMER(i), and DL_PathlossChange(i) may be used.

The following are examples of reporting parameter configurations.

Type 2 PH and Type 4 PH may be reported less frequently than Type 1 PHand Type 3 PH. Some or all of the reporting parameters(PROHIBIT_PHR_TIMER(i), PERIODIC PHR TIMER(i), and DL_PathlossChange(i))for Type 2 and Type 4 are larger than those for Type 1 and Type 3. Alarger PROHIBIT_PHR_TIMER(i) value means that the time between anevent-triggered PHR (i.e., triggered by change of pathloss) and the lastPHR may be larger. A larger PERIODIC PHR TIMER(i) value means that thetime between two periodic PHRs may be larger. A largerDL_PathlossChange(i) value means that the change of the DC pathloss maybe larger to trigger a (non-periodic) PHR.

Type 1 PH may be reported more frequently than Type 3 PH in cases wherethe maximum WTRU transmit power limit is the sum of WTRU transmit poweracross all carriers. In this case, some or all of the parameters(PROHIBIT_PHR_TIMER(i), PERIODIC PHR TIMER(i), and DL_PathlossChange(i))for Type 3 PH are larger than those for Type 1 PH.

Type 3 PH may be reported more frequently than Type 1 PH in cases wherethe maximum WTRU transmit power limit is per carrier (or carrier group)instead of across all carriers. In this case, some or all of theparameters (PROHIBIT_PHR_TIMER(i), PERIODIC PHR TIMER(i), andDL_PathlossChange(i)) for Type 1 PH are larger than those for Type 3 PH.

In regard to the periodicity of the different PHR types, the eNodeB maydefine each PHR type and may set the reporting periodicity of each typeas needed. The frequency and the type of reporting relates tofunctionality of the eNodeB's scheduler.

For PH defined over several carriers (for example, the wideband PH orcarrier group-specific PH), a pathloss metric called equivalentpathloss, PL_(eq), may be used for PH reporting. The equivalent pathlossmay be any one of following: the maximum (or minimum) pathloss amongcarriers of interest, the average pathloss of carriers of interest, orthe weighted average of pathloss among carriers of interest.

Pathloss of each carrier may be weighted by its contribution to thetotal WTRU calculated transmit power (among all carriers or a group ofcarriers). The pathloss may be weighted by the following factors: thebandwidth of the PUSCH resource assignment on each carrier expressed inthe number of resource blocks valid for subframe i, a transport formatfactor, and a transmit power adjustment step (according to an UL powercontrol command) for subframe i. The transport format factor isdetermined by: Δ_(TP)(i)=10log_(t0)(2^(MPB(i)×K) _(s−)1) for K_(s)=1.25and Δ_(TF)(i)=0 for K_(s)=0 where Ks is a cell specific parameter givenby RRC.

${{MPR}(i)} = \frac{{TBS}(i)}{N_{RE}(i)}$

where TBS(i) is the transport block size for subframe i and N_(RE)(i) isthe number of resource elements.

Wideband Power Headroom Reporting Procedures

For the case of wideband PH reporting, one PROHIBIT_PHR_TIMER(i) and onePERIODIC PHR TIMER(i) maybe maintained (e.g., start, running,expiration, restart) for WB-PHR type for the entire cell bandwidth.

A PHR of Type i may be triggered if any of the following events occur.

1. The PROHIBIT_PHR_TIMER(i) expires or has expired and the pathloss haschanged more than DL_PathlossChange(i) dB since the last PHR. Forwideband PHR, the pathloss used for PHR triggering is the PL_(eq)defined above.

2. The PERIODIC PHR TIMER(i) expires, in which case the PHR is referredto as a “Periodic PHR.”

3. Upon configuration and reconfiguration (or reset) of a Periodic PHR.

If the PH reporting procedure determines that a PHR of Type i has beentriggered since the last transmission of a PHR of the same type and ifthe WTRU has UL resources allocated for new transmission for this TTI,then the method 200 as shown in FIG. 2 may be performed.

The PH value is obtained from the physical layer (step 202). TheMultiplexing and Assembly procedure in the MAC is instructed to generatea PHR MAC CE based on the obtained PH value (step 204). A determinationis made whether the PHR is a Periodic PHR (step 206). If the PHR is aPeriodic PHR, then restart the PERIODIC PHR TIMER(i) (step 208). If thePHR is not a Periodic PHR (step 206) or after restarting the PERIODICPHR TIMER(i) (step 208), restart the PROHIBIT_PHR_TIMER(i) (step 210).The method then terminates.

Even if multiple events for one type WB-PHR occur by the time a PHR maybe transmitted, one PHR per type is included in the MAC PDU.

Carrier-Specific or Carrier Group-Specific Power Headroom ReportingProcedures

In another example, for the case of carrier-specific and carriergroup-specific PH reporting, one PROHIBIT_PHR_TIMER and one PERIODIC PHRTIMER are maintained for each CS-PHR Type for each carrier or carriergroup. Within the same type, the PH reporting procedure of one carrieror carrier group is independent of other carriers or carrier groups.

A PHR of Type i of each carrier or carrier group may be triggered if anyof the following events occur.

1. The PROHIBIT_PHR_TIMER(i) of this carrier or carrier group expires orhas expired and the pathloss has changed more than DL_PathlossChange(i)dB since the last PHR of Type i of this carrier or carrier group. Forcarrier-specific PH, the pathloss follows the same definition as in LTE.For carrier group-specific PH, the pathloss is the PL_(eq) definedabove.

2. The PERIODIC PHR TIMER(i) of this carrier or carrier group expires,in which case the PHR is referred to as “Periodic PHR.”

3. Upon configuration and reconfiguration (or reset) of a Periodic PHR.

If the PH reporting procedure determines that a PHR of Type i for thiscarrier or carrier group has been triggered since the last transmissionof a PHR of the same type and if the WTRU has UL resources allocated fornew transmission for this TTI, then the method 300 as shown in FIG. 3 isperformed.

The PH value is obtained from the physical layer (step 302). TheMultiplexing and Assembly procedure in the MAC is instructed to generatea PHR MAC CE based on the obtained PH value (step 304). A determinationis made whether the PHR is a Periodic PHR (step 306). If the PHR is aPeriodic PHR, then restart the PERIODIC PHR TIMER(i) for this carrier orcarrier group (step 308). If the PHR is not a Periodic PHR (step 306) orafter restarting the PERIODIC PHR TIMER(i) (step 308), restart thePROHIBIT_PHR_TIMER(i) for this carrier or carrier group (step 310). Themethod then terminates.

Even if multiple events for one type PHR for one carrier or carriergroup occur by the time a PHR may be transmitted, only one PHR per typeper carrier or carrier group may be included in the MAC PDU. Butmultiple PHRs of the same type or different types may be included in theMAC PDU (the header of MAC PDU implies MAC CE, then one MAC CE may alsoconcatenate multiple control commands, e.g., multiple PHRs).

The PHR may alternatively be triggered by the WTRU sending a bufferstatus report (BSR) and if the Periodic PHR is not currently running.Only one BSR value is reported for the WTRU, regardless of the number ofUL carriers. In one instance, a BSR may be sent when the WTRU has a ULgrant and the BSR informs the eNodeB of the buffer status. If the numberof padding bits on the PUSCH is equal to or larger than the size of theone configured PHR type plus its subheader, at least one PHR type isreported on the PUSCH along with the BSR, instead of sending the paddingbits. Sending the PHR along with the BSR provides the eNodeB with a morecomplete picture of the current status at the WTRU so that the eNodeBscheduler may take more appropriate action. Also when the BSR is empty,the WTRU may transmit one or several PHRs (wideband type,carrier-specific type, or carrier group-specific type) in place of theBSR, instead of sending an empty BSE on the PUSCH. The PHR may be set tothe report mode according to the requested resource in the BSR and thePH reported is the momentary PH value calculated for the report.

Exemplary LTE System Configuration

FIG. 4 shows a Long Term Evolution (LTE) wireless communicationsystem/access network 400 that includes an Evolved-Universal TerrestrialRadio Access Network (E-UTRAN) 405. The E-UTRAN 405 includes a WTRU 410and several evolved Node-Bs, (eNBs) 420. The WTRU 410 is incommunication with an eNB 420. The eNBs 420 interface with each otherusing an X2 interface. Each of the eNBs 420 interface with a MobilityManagement Entity (MME)/Serving Gate Way (S-GW) 430 through an S1interface. Although a single WTRU 410 and three eNBs 420 are shown inFIG. 4, it should be apparent that any combination of wireless and wireddevices may be included. In the wireless communication system accessnetwork 400.

FIG. 5 is an exemplary block diagram of an LTE wireless communicationsystem 500 including the WTRU 410, the eNB 420, and the MME/S-GW 430. Asshown in FIG. 5, the WTRU 410, the eNB 420 and the MME/S-GW 430 areconfigured to perform a method of uplink power headroom reporting forcarrier aggregation.

In addition to the components that may be found in a typical WTRU, theWTRU 410 includes a processor 516 with an optional linked memory 522, atleast one transceiver 514, an optional battery 520, and an antenna 518.The processor 516 is configured to perform a method of uplink powerheadroom reporting for carrier aggregation. The transceiver 514 is incommunication with the processor 516 and the antenna 518 to facilitatethe transmission and reception of wireless communications. In case abattery 520 is used in the WTRU 410. it powers the transceiver 514 andthe processor 516.

In addition to the components that may be found in a typical eNB, theeNB 420 includes a processor 517 with an optional linked memory 515,transceivers 519, and antennas 521. The processor 517 is configured toperform a method of uplink power headroom reporting for carrieraggregation. The transceivers 519 are in communication with theprocessor 517 and antennas 521 to facilitate the transmission andreception of wireless communications. The eNB 420 is connected to theMobility Management Entity/Serving GateWay (MME/S-GW) 430 which includesa processor 533 with an optional linked memory 534.

Although features and elements are described above in particularcombinations, each feature or element may be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller. Application Specific integrated Circuits (ASICs),Application Specific Standard Products (ASSPs); Field Programmable GateArrays (PPGAs) circuits, any other type of integrated circuit (IC),and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station. Mobility ManagementEntity (MME) or Evolved Packet Core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a Software Defined Radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a Near Field Communication (NFC)Module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

1. A method for reporting a carrier-specific power headroom, comprising: calculating a maximum power per carrier, P_(CMAX) _(—) _(carrier); on a condition that the carrier has a valid uplink grant, calculating the power headroom according to the formula: PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—) _(UG)(k,i) where k is a carrier number, i is a subframe number in which the carrier has a valid uplink grant, and P_(PUSCH) _(—) _(UG)(k,i) is a transmit power for carrier k in subframe i prior to imposing maximum power limitations; and reporting the calculated power headroom.
 2. The method according to claim 1, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{{k = 1},K,K}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, K is a maximum number of carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 3. The method according to claim 2, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k is limited by P_(CMAX) such that ${\sum\limits_{{k = 1},K,K}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 4. The method according to claim 1, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω is a set of active carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for a subset of earners that have an active grant in subframe i for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 5. The method according to claim 4, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω is limited by P_(CMAX) such that ${\sum\limits_{k \in \Omega}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 6. The method according to claim 1, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega_{m}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}$ where BW_(k) is the hand width for carrier k, Ωm is a set of carriers of carrier group m, and P_(CMAX)(m) is a maximum transmit power for carrier group m.
 7. The method according to claim 6, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω_(m) is limited by P_(CMAX)(m) such that ${\sum\limits_{k \in \Omega_{m}}{P_{{CMAX}\_ {carrier}}(k)}} \leq {{P_{CMAX}(m)}.}$
 8. The method according to claim 1, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in {\Omega_{m}\bigcap\; {carrierkhasgrant}}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω_(m) is a set of carriers of carrier group m, and P_(CMAX)(m) is a maximum transmit power for carrier group m.
 9. The method according to claim 8, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω_(m) is limited by P_(CMAX)(m) such that ${\sum\limits_{k \in {\Omega_{m}\bigcap\; {carrierkhasgrant}}}{P_{{CMAX}\_ {carrier}}(k)}} \leq {{P_{CMAX}(m)}.}$
 10. A method for reporting a carrier-specific power headroom, comprising: calculating a maximum power per carrier, P_(CMAX) _(—) _(carrier); on a condition that the carrier has a valid uplink grant, calculating the power headroom according to the formula: PH(k,i)=P _(CMAX) _(—) _(carrier)(k)−P _(PUSCH) _(—) _(UG)(k,i) where k is a carrier number, i is a subframe for which the power headroom is to be reported, and P_(PUSCH) _(—) _(REP)(k,i) is defined as P _(PUSCH) _(—) _(REF)(k,i)=f ₁ _(—) _(REF)(P _(PUSCH) _(—) _(REF)(n,i))+α×(PL(k)−f ₂ _(—) _(REF)(PL(n))) where f₁ _(—) _(REF)(*) is a function of a reference carrier-specific wireless transmit/receive unit transmit power, n≠k and carrier n belongs to the set of carriers with a valid uplink grant, α is a cell-specific parameter, PL(k) is a pathloss estimate on carrier k, and f₂ _(—) _(REF)(*) is a function of a reference carrier-specific pathloss; and reporting the calculated power headroom.
 11. The method according to claim 10, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{{k = 1},K,K}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) the bandwidth for carrier k, K is a maximum number of carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 12. The method according to claim 11, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k is limited by P_(CMAX) such that ${\sum\limits_{{k = 1},K,K}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 13. The method according to claim 10, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω is a set of active carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for a subset of carriers that have an active grant in subframe i for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 14. The method according to claim 13, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω is limited by P_(CMAX) such that ${\sum\limits_{k \in \Omega}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 15. The method according to claim 10, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega_{m}}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}{(m)}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω_(m) is a set of carriers of carrier group m, and P_(CMAX)(m) is a maximum transmit power for carrier group m.
 16. The method according to claim 15, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω_(m) is limited by P_(CMAX)(m) such that ${\sum\limits_{k \in \Omega_{m}}{P_{{CMAX}\_ {carrier}}(k)}} \leq {{P_{CMAX}(m)}.}$
 17. A method for reporting a carrier group-specific power headroom, comprising: calculating a maximum power per carrier, P_(CMAX) _(—) _(carrier)(k); on a condition that at least one carrier in the carrier group has a valid uplink grant, calculating the group power headroom according to the formula: ${{PH}\left( {m,i} \right)} = {{10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}$ where m is a carrier group number, i is a subframe number in which at least one carrier in the carrier group has a valid uplink grant, Ω_(m) is a set of carriers of carrier group m, and P_(PUSCH) _(—) _(UG)(k,i) is a transmit power for carrier k in subframe i prior to imposing maximum power limitations; and reporting the calculated power headroom.
 18. The method according to claim 17, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{{k = 1},K,K}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, K is a maximum number of carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 19. The method according to claim 18, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k is limited by P_(CMAX) such that ${\sum\limits_{{k = 1},K,K}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 20. The method according to claim 17, wherein calculating the maximum power par carrier is based, on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω is a set of active carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for a subset of carriers that have an active grant in subframe i for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 21. The method according to claim 20, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω is limited by P_(CMAX) such that ${\sum\limits_{k \in \Omega}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 22. A method for reporting a carrier group-specific power headroom, comprising: calculating a maximum power per carrier, P_(CMAX) _(—) _(carrier)(k); on a condition that no carrier in the carrier group has a valid uplink grant, calculating the group power headroom using a reference grant according to the formula: ${{PH}\left( {m,i} \right)} = {{10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{CMAX}\_ {carrier}}{(k)}}{10}}} \right)}} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {REF}}{({k,i})}}{10}}} \right)}}}$ where m is a carrier group number, i is a subframe number for which the power headroom is to be reported, Ω_(m) is a set of carriers of carrier group m, and P_(PUSCH) _(—) _(REF)(k,i) is defined as P _(PUSCH) _(—) _(REF)(k,i)=f ₁ _(—) _(REF)(P _(PUSCH) _(—) _(REF)(n,i))+α×(PL(k)−f ₂ _(—) _(REF)(PL(N))) where f₁ _(—) _(REF)(*) is a function of a reference carrier-specific WTRU transmit power, n≠k and carrier n belongs to the set of carriers with a valid uplink grant, α is a cell-specific parameter, PL(k) is a pathloss estimate on carrier k, and f₂ _(—) _(REF)(*) is a function of a reference carrier-specific pathloss; and reporting the calculated power headroom.
 23. The method according to claim 22, wherein, calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{{k = 1},K,K}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, K is a maximum number of carriers, P_(CMAX) is a total maximum transmit power, and the formula is used far all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 24. The method according to claim 23, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k is limited by P_(CMAX) such that ${\sum\limits_{{k = 1},K,K}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 25. The method according to claim 22, wherein calculating the maximum power per carrier is based on the formula: ${P_{{CMAX}\_ {carrier}}(k)} = {10\; {\log_{10}\left( {\left( \frac{{BW}_{k}}{\sum\limits_{k \in \Omega}{BW}_{k}} \right) \times 10^{\frac{P_{CMAX}}{10}}} \right)}}$ where BW_(k) is the bandwidth for carrier k, Ω is a set of active carriers, P_(CMAX) is a total maximum transmit power, and the formula is used for a subset of carriers that have an active grant in subframe i for all sub-bands or carriers across all power amplifiers at a wireless transmit/receive unit.
 26. The method according to claim 4, wherein the sum of P_(CMAX) _(—) _(carrier)(k) for all carriers k in Ω is limited by P_(CMAX) such that ${\sum\limits_{k \in \Omega}{P_{{CMAX}\_ {carrier}}(k)}} \leq {P_{CMAX}.}$
 27. A method for reporting a carrier group-specific power headroom, comprising: on a condition that at least one carrier in the carrier group has a valid uplink grant, calculating the group power headroom according to the formula: ${{PH}\left( {m,i} \right)} = {{P_{CMAX}(m)} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {UG}}{({k,i})}}{10}}} \right)}}}$ where m is a carrier group number, i is a subframe number in which at least one carrier In the carrier group has a valid uplink grant, Ω_(m) is a set of carriers of carrier group m, P_(CMAX)(m) is a configured maximum allowed wireless transmit/receive unit (WTRU) transmit power for carrier group m, and P_(PUSCH) _(—) _(UG)(k,i) is a transmit power for carrier k in subframe i prior to imposing maximum power limitations; and reporting the calculated power headroom.
 28. A method for reporting a carrier group-specific power headroom, comprising: on a condition that no carrier in the carrier group has a valid uplink grant, calculating the group power headroom using a reference grant according to the formula: ${{PH}\left( {m,i} \right)} = {{P_{CMAX}(m)} - {10\; {\log_{10}\left( {\sum\limits_{k \in \Omega_{m}}10^{\frac{P_{{PUSCH}\_ {REF}}{({k,i})}}{10}}} \right)}}}$ where m is a carrier group number, i is a subframe number for which the power headroom is to be reported, Ω_(m) is a set of carriers of carrier group m, P_(CMAX)(m) is a configured maximum allowed wireless transmit/receive unit (WTRU) transmit power for carrier group m, and P_(PUSCH) _(—) _(REF)(k,i) is defined as P _(PUSCH) _(—) _(REF)(k,i)=f ₁ _(—) _(REF)(P _(PUSCH) _(—) _(REF)(n,i))+α×(PL(k)−f ₂ _(—) _(REF)(PL(n))) where f₁ _(—) _(REF)(*) is a function of a reference carrier-specific WTRU transmit power, n≠k and carrier n belongs to the set of carriers with a valid uplink grant, α is a cell-specific parameter, PL(k) is a pathloss estimate on carrier k, and f₂ _(—) _(REF)(*) is a function of a reference carrier-specific pathloss; and reporting the calculated power headroom.
 29. A method for reporting a carrier-specific power headroom, comprising: calculating a maximum power per carrier, P_(CMAX) _(—) _(carrier); on a condition that the carrier has a valid uplink grant, calculating the power headroom for a given carrier, k, in a given subframe, i, in which the carrier k has a valid uplink grant based on P_(CMAX) _(—) _(carrier) and a transmit power for the carrier k in the subframe i prior to imposing maximum power limitations; and reporting the calculated power headroom. 